Polyvinyl chloride (“PVC”) is in wide commercial use because of its superior performance and properties. Modern consumers utilize PVC-containing products throughout their daily activities, since it is a primary ingredient in profiles, sidings, floorings, films/sheets, fabrics, pipes, fittings and fabrics. Various additives, such as heat stabilizers are commonly included when formulating compositions containing PVC. Heat stabilizers are required because as PVC is heated to temperatures of 160° C. and above, decomposition reactions begin, where the polymer releases HCl. As such decomposition continues, unstable structures are formed, which further accelerate HCl elimination and decomposition. Efforts have been ongoing to develop improved heat stabilizers.
U.S. Pat. No. 8,198,352 discloses that tin-based stabilizers are used in chlorine-containing polymers and copolymers, such as PVC. The tin-based stabilizers are used as mixtures of mono-alkyltin with di-alkyltin compounds of the same alkyl group, such as mixtures of mono- and dimethyltin compounds, mono- and di-butyltin compounds or mono- and di-octyltin compounds. Tri-alkyltin compounds are known to be inefficient as heat stabilizers and their concentration in the stabilizers is usually less than 1%.
EP 2123659 discloses high purity mono-alkyltin compounds containing mono-alkyltin compounds of 95-99.99% purity, 0.01-0.5% dialkyltin compounds and 0.01-0.5% tri-alkyltin compounds.
U.S. Pat. No. 4,496,490 discloses the preparation of high purity mono-octyltin thioglycolate heat stabilizers starting from mono-octyltin chloride of 99.2% purity. While the product contained up to 5% tri-octyltin iso-octylmercaptoacetate, the presence of di-octyltin compounds in the final product was not reported.
U.S. Pat. No. 4,193,913 discloses high purity mono-alkyltin stabilizers prepared using mono-methyl-, mono-butyl or mono-octyltin chlorides as raw materials, and reacting those with thioglycolate esters. Purity of the chlorides was not specified.
EP 1743898 discloses preparation of mono-alkyltin and dialkyltin chlorides. While di-octyltin chloride was obtained at the purity of greater than 98%, purity of the mono-alkyltinchloride was not measured.
EP 1225177 discloses preparation of mono-alkyl in halides at greater than 60% yield, using a variety of catalysts.
GB 1510973 discloses preparation of mono-octyltin thioglycolate stabilizers using mono-octyltin chloride of 99.2% purity. Purity of the prepared mono-octyltin stabilizer was not measured or disclosed.
U.S. Pat. No. 4,052,427 discloses the preparation of dialkyltin halides and mixed dialkyltin halides, and the corresponding mixed di-alkyltin stabilizer compounds. Nevertheless, a continuing need exists for more effective, non-toxic alkyltin heat stabilizer compositions for chlorine-containing polymers.